1. Field of the Invention
The present invention generally relates to electron beam recorders, electron beam irradiation position detecting methods and electron beam irradiation position controlling methods and more particularly, to an electron beam recorder, an electron beam irradiation detecting method and an electron beam irradiation position controlling method, in which signals are spirally recorded on a master of an information recording medium such as an optical disc highly accurately.
2. Description of the Prior Art
In general, manufacture of an optical disc includes a step in which by using an optical disc master recorder employing a laser or an electron beam as a light source, a master coated with photoresist is exposed and developed such that an optical disc master formed, on its surface, with concave and convex patterns such as information pits and grooves is produced, a step of producing a metallic die which has the concave and convex patterns transferred thereto from the optical disc master and is called a “stamper”, a step of producing a resinous molded substrate by using the stamper and a step in which a recording film, a reflective film, etc. are formed on the molded substrate.
An electron beam recorder used for exposure at the time an optical disc master is produced by using an electron beam is generally arranged as follows. FIG. 7 shows an arrangement of a conventional electron beam recorder. The conventional electron beam recorder includes an electron beam source 601 for generating an electron beam 614 and an electron optical system 602 which converges the emitted electron beam 614 onto a resist master 609 so as to record information patterns on the resist master 609 in accordance with inputted information signals. The electron beam source 601 and the electron optical system 602 are accommodated in a vacuum chamber 613.
The electron beam source 601 is constituted by a filament for emitting electrons upon flow of electric current therethrough, an electrode for suppressing the emitted electrons, an electrode for extracting and accelerating the electron beam 614, etc. and is adapted to emit the electrons from one point.
Meanwhile, the electron optical system 602 includes a lens 603 for converging the electron beam 614, an aperture 604 for determining a beam diameter of the electron beam 614, a pair of first deflection electrodes 605 and a pair of second deflection electrodes 606 which deflect the electron beam 614 in orthogonal directions, respectively in accordance with the inputted information signals, a shielding plate 607 for shielding the electron beam 614 bent by the first deflection electrodes 605 and a lens 608 for converging the electron beam 614 onto a surface of the resist master 609.
Furthermore, the resist master 609 is held on a rotary stage 610 and is moved horizontally together with the rotary stage 610 in the direction of the arrow by a horizontally traveling stage 611. If the master 609 is moved horizontally by the horizontally traveling stage 611 while being rotated by the rotary stage 610, the electron beam 614 can be irradiated spirally on the master 609 so as to spirally record the information signals of the optical disc on the master 609.
In addition, a focusing grid 612 is disposed substantially flush with the surface of the master 609. This focusing grid 612 is provided for adjusting a focal position of the lens 608 such that the lens 608 converges the electron beam 614 onto the surface of the master 609. If electrons reflected by the focusing grid 612 or secondary electrons emitted from the focusing grid 612 upon irradiation of the electron beam 614 on the focusing grid 612 are detected by a detector such that a grid image is monitored, the focal position of the lens 608 can be adjusted from a state in which the grid image is seen. The members 609-612 referred to above are also accommodated in the vacuum chamber 613.
The first deflection electrodes 605 are provided for bending the electron beam in a direction substantially perpendicular to a travel direction of the horizontally traveling stage 611. Since the first deflection electrodes 605 bend the electron beam 614 towards the shielding plate 607 in accordance with signals inputted to the first deflection electrodes 605, the first deflection electrodes 605 are capable of selecting whether or not the electron beam 614 is irradiated on the master 609 such that information pit patterns, etc. can be recorded on the master 609.
Meanwhile, the second deflection electrodes 606 are provided for bending the electron beam 614 in a direction substantially perpendicular to that of the first deflection electrodes 605, namely, in the substantially same direction as the travel direction of the horizontally traveling stage 611 and is capable of bending the electron beam 614 in the substantially same direction as the travel direction of the horizontally traveling stage 611 in accordance with signals inputted to the second deflection electrodes 606. The travel direction of the horizontally traveling stage 611 corresponds to a radial direction of the master 609 to be recorded. Variations of a track pitch of the optical disc, etc. can be corrected by the signals inputted to the second deflection electrodes 606.
In the optical disc, since the track pitch of information signal pits to be recorded is required to be recorded highly accurately, travel amount of the horizontally traveling stage 611, nonrepeatable runout of the rotary stage 610 or variations of irradiation position of the electron beam 614 should be controlled with high precision. As disclosed in, for example, Japanese Patent Laid-Open Publication No. 2002-141012, error of the travel amount of the horizontally traveling stage 611 or the like can be detected by laser measurement, etc. so as to be eliminated by driving the second deflection electrodes 606.
In the conventional electron beam recorder, even if mechanical accuracies such as the travel amount of the horizontally traveling stage 611 and the nonrepeatable runout of the rotary stage 610 can be corrected, position of the electron beam 614 itself is most likely to vary and thus, it is of vital importance to correct variations of the position of the electron beam 614. The variations of the position of the electron beam 614 are caused by a phenomenon in which the electron beam 614 undergoes great influences such as variations of magnetic field around the recorder as well as mechanical vibrations, acoustic noise and electrical noise of the recorder.
Generally, since the electron beam source 601 and the electron optical system 602 are accommodated in the vacuum chamber 613, it is quite difficult to detect in the vacuum chamber 613 the variations of the position of the electron beam 614 subjected to acceleration and convergence. Meanwhile, a method may be considered in which the electron beam 614 used for recording is irradiated on a detection object other than the master 609, for example, the focusing grid 612 and variations of irradiation position of the electron beam 614 on the detection object are detected by using signals of a detector for detecting an image formed on the detection object. However, this method is not applicable when signals are being recorded on the master 609. Therefore, even in this method, it is extremely difficult to detect and correct the variations of the position of the electron beam 614 when the signals are being recorded on the master.